While Marvel's First Family gained their amazing abilities from cosmic radiation after a mission in space, the MCU's MCU's Mister Fantastic and his family could have a unique origin that still plays on their history of exploration and science. This small chance could help the team fit into the currently established MCU timeline as well.
After the first two Ant-Man films, it's been confirmed that the Quantum Realm is a universe that can be entered on the microscopic level using Pym Particles. Existing as a reality where time works very differently, travel through the Quantum Realm is instrumental in Avengers: Endgame, allowing Earth's Mightiest Heroes to travel back in time and retrieve the Infinity Stones from the past. It's also where Janet van Dyne was trapped for 30 years, having learned to survive while also gaining new abilities. This importance may continue with The Fantastic Four's debut in the MCU.
The Fantastic Four Can Get Powers From The Quantum Realm Instead Of Space
The Fantastic Four having their accident while attempting to travel the Quantum Realm rather than space would strongly tie the family to the greater MCU right off the bat. Whether the full Fantastic Four are introduced in an earlier film (like Ant-Man 3) or in their own movie set to release in early 2025, gaining their abilities from the Quantum Realm or a Kang encoutner would be very exciting. It would also make use of an established convention already familiar to audiences.
As seen in the trailer for Ant-Man and the Wasp: Quantumania, it's been revealed that there are full civilizations in the Quantum Realm with a whole range of different beings of all shapes and sizes. It also looks to be the home of the time-traveling despot Kang the Conqueror, and perhaps the Time Variance Authority. As such, it's possible the Fantastic Four may have been exploring the Quantum Realm unbeknownst to Pym.
The Quantum Realm Can Help The Fantastic Four Avoid An Origin Story Problem
Connecting the Quantum Realm to The Fantastic Four would also help circumvent the need to go through their origins again. At this point, previous iterations of the First Family on-screen have already covered how they got their powers and became a family unit quite well. Likewise, the team is at its most interesting when they're more experienced and have room to play upon existing family dynamics. As such, debuting them as brand-new active MCU heroes would make that difficult.
That being said, introducing The Fantastic Four as established heroes doesn't make sense either due to their absence from the last 15 years of the MCU, so the Quantum Realm can provide the solution. If they've been stuck in the Quantum Realm, where time is different, they could have been trapped for decades away from the public eye, like when Scott Lang's Ant-Man was trapped in the Quantum Realm before Avengers: Endgame. He was been stuck for five years while only experiencing about five hours. As such, it wouldn't be surprising if Ant-Man 3 sets the foundation for Marvel's Fantastic Four when it releases on February 17th.
